1. Field Of The Invention
The invention relates to flash photography for a fixed-focus camera. More particularly, the invention provides apparatus, responsive to an indication of a close-up subject, for improving depth of field and flash exposure control for close-up flash photography.
2. Description Of The Prior Art
A camera provides an acceptably focused image of subjects within its depth of field. For a fixed-focus camera having lens apparatus focused at its hyperfocal distance, all subjects beyond a near distance, which is one-half the hyperfocal distance, appear in focus. To further reduce the near distance, and thereby increase depth of field, fixed-focus cameras use a lens of relatively small maximum aperture. However, a small aperture limits an ambient exposure with a hand-held camera to relatively high ambient light conditions, and limits a flash exposure to relatively short-range subjects.
A notable exception to a fixed-focus camera having these limitations is the disc 4000 camera manufactured by the Eastman Kodak Company of Rochester, N.Y. and disclosed in U.S. Pat. No. 4,361,387, which is commonly assigned herewith. This camera (and other disc cameras manufactured by Eastman Kodak) has optics of relatively short focal length, e.g. 12.5 millimeters, and therefore has a relatively large maximum exposure aperture, e.g. f/2.8. Additionally, this disc camera takes advantage of the wide exposure latitude of color print film to allow fully automatic exposure control with a simple exposure control system by providing only two exposure settings, e.g. 1/200 of a second at f/6 when ambient light is above 125 foot-lamberts, and 1/100 of a second at f/2.8 with flash illumination when ambient is below 125 foot-lamberts.
At f/2.8, the minimum acceptable distance for a subject in focus is approximately 1.2 meters, whereas at f/6 a subject as close as 0.6 meter is acceptably focused. In low light conditions when the f/2.8 aperture and flash illumination are used, a subject closer to the camera than the minimum depth of field would be not only out of focus but may also be overexposed, because of the relation between flash illumination and subject distance. Because the exposure setting and the flash decision are made automatically, a photographer may not know which exposure mode will be selected. For a close-up subject in marginal ambient light, the photographer may take an unacceptable flash picture or may decide not to take a picture, when in fact an acceptable ambient exposure would occur.